Our invention generally relates to fiber optics and specifically to methods and systems for accessing fractured fibers in fiber optic connectors, more specifically fiber optic connector ferrules.
Ubiquitous deployment of fiber optic technology has increased the bandwidth and reliability of modern communication networks well beyond prior limits for copper and other competing technologies. A single fiber optic cable when installed in a network replaces thousands of copper lines. In fact, optical fibers are not considered to be bandwidth-limited. Despite the tremendous improvement in performance over the technology it replaced and continues to replace, fiber optic technology does present some problems.
Of particular import to the present invention is the problem of determining the root cause of mechanical failures in a fiber optic connector. Mechanical integrity of optical fibers is an essential element of assuring long-term reliable performance of fiber optic telecommunications networks. Loss of this mechanical integrity leads eventually to transmission failures in fiber optic network components such as cables, connectors and devices that make up the modern broadband telecommunications networks. When fiber mechanical failures occur, one needs to find the cause of such mechanical failures and determine the conditions under which these failures occur. Primary means of investigating fiber mechanical failures involves detailed examination of fiber fracture surfaces to find telltale signs of fracture events with clues to the mechanical forces involved, the geometry within which these forces might act on the fibers, and the magnitude of these forces. This detailed examination is known as fractography or break source analysis of fiber fracture surfaces.
In connectorized optical fibers, fiber breaks that take place within the connector body are not readily accessible for fractography. In fact, fiber fractures in connectors have often gone without any definitive fractography examination. As the bandwidth and capacity of modern telecommunications networks increase at an accelerating pace, it has become critically important to investigate even occasional fiber breaks in connectors due to its potentially high negative impact on both service providers"" business and subscribers"" communications needs.
In particular, and with reference to FIG. 1, a connector 100 generically consists of a metal base 110 and a ferrule 120. The ferrule 120 includes a central cylindrical opening or capillary 122 (typically having a 126-xcexcm diameter). The capillary 122 is filled with an adhesive resin or epoxy fill 123 and a stripped and cleaned fiber 124 (typically having a 125-xcexcm diameter) is inserted into the capillary 122. The adhesive resin 123 also fills the entry cone 128 and rear opening 130 of the connector along with the coated (unstripped) portion of the fiber 132 as is shown in FIG. 1. The adhesive is, then, cured, and, the fiber/ferrule tip 134 is polished to give a radiused surface. A connector assembly is then formed when two ferrule-fiber assemblies are mated and brought into physical contact on their polished surfaces. The adhesive in the capillary 122 (about 0.5-xcexcm thickness between the ferrule and the fiber) serves to fix the fiber with respect to the ferrule and maintain the physical contact. Therefore, dimensional and mechanical stability of the ferrule-fiber assembly is critically important for satisfactory long-term performance and reliability of fiber optic PC connectors.
The prior art is devoid of methods and systems for extracting the bare and coated fiber from the connector without compromising the evidence that is critical to root cause analysis. Accordingly, the prior art does not allow for fractographic examination of fiber breaks if those breaks take place in the connector, in particular in the ferrule capillary. It is therefore an object of the present invention to provide a method and apparatus that enables fractographic examination of broken fibers to determine the root cause of fiber mechanical failures in connectors and devices.
Our invention is a method and apparatus for extracting a fiber from a connector. In accordance with our invention, methods are presented to remove the metallic housing, adhesive bead/block near the ferrule entry cone and the annular adhesive film within the ferrule. Further, in accordance with our method, the fiber is extracted from the connector thereby allowing fratographic examination by Scanning Electron Microscopy (SEM).
Specifically, the process begins with removal of the metallic housing of the ferrule fiber assembly by a first acid-etching process wherein the acid bath is a mixture of hydrochloric acid and nitric acid. With the metallic housing removed, the ferrule-fiber assembly is then immersed in a bath of sulfuric acid, i.e., a second etching, is done to remove or loosen the adhesive resin in the ferrule capillary and back opening. After each acid-etching step, the ferrule-fiber assembly is rinsed with distilled water. Finally, localized heating is applied to the ferrule while a tensile load is applied to the fiber. The fiber is then extracted from the ferrule as a result of the localized heating and load application. If application of the tensile load and localized heating initially fails to extract the fiber, then the ferrule may be re-immersed in the solution of the second acid etching. The localized heating and application of the tensile load may then be repeated. Of course, localized heating under the force of the tensile load and the immersion into the sulfuric acid may be alternately repeated until extraction is successful.
Our invention advantageously allows for nondestructive extraction of the fiber from the ferrule so that further examination can be done of the fiber to determine the root cause of failures that occur as a result fractures of the fiber in the ferrule capillary.